(1) Field of the Invention
The present invention relates to a method of utilizing multiple schedules to provide linear thrust in response to linear throttle movements. More particularly, the present invention relates to a method of altering the operation of a gas turbine engine in response to throttle adjustments to produce a thrust response linearly related to such throttle adjustments.
(2) Description of the Related Art
Linear thrust response vs. throttle position is highly desirable to military pilots attempting precise maneuvers such as refueling or attempting to land on an aircraft carrier deck. Current methods of controlling a gas turbine engine allow linear thrust vs. throttle position to be scheduled at one flight condition (such as a carrier landing) but cannot maintain thrust linearity over a range of other critical flight conditions, such as refueling.
The shortcoming of the current method is rooted in the fact that a single characteristic of engine inlet corrected airflow (W2R) increase vs. thrust increase is used as a control schedule for all flight conditions. As each flight condition has its own unique values of idle and intermediate inlet airflows, engine thrust is typically very non-linear vs. inlet airflow.
FIG. 1 is a logic diagram illustrating the current method of scheduling part power inlet airflow at any flight condition for known idle and intermediate inlet airflows. The illustrated method requires the inputting of the throttle position (FNRQ), the idle power scheduled airflow (W2RID), and the intermediate power scheduled airflow (W2RINT). At step 1, there is utilized a schedule 11 used to schedule engine airflow comprised of a plot of the part power index (PLAIDX) as a function of the FNRQ. The inputted FNRQ measured at any time during an engine's operation is used as an index to the schedule 11 of step 1 and PLAIDX is outputted. This outputted PLAIDX is combined with the W2RID and the W2RINT to calculate a part power scheduled airflow (W2RSCH) according to the equation W2RSCH=W2RID+PLAIDX (W2RINT−W2RID). The calculated W2RSCH is utilized to add or subtract fuel flow to the engine in order to obtain a linear airflow giving rise to a predominantly linear thrust response to the movement of the throttle position.
Variations of this method involving engine fan speed are also possible due to the unique relationship between inlet flow and fan speed. The method described above provides a relatively linear thrust in response to linear movements of the throttle under certain well defined operating constraints. However, this method fails to produce a substantially linear thrust response over a broad range of operating conditions.
What is therefore needed is a method of achieving approximately linear thrust from idle power to intermediate power (i.e. maximum non-augmented thrust) at any flight condition.